Pre-term labor or pre-term birth is a significant problem that costs billions of health care dollars annually. An infant is considered pre-term if born before thirty-seven weeks of gestation. Of the estimated 6,250,000 pregnancies that occur in the U.S. each year, about 11% are pre-term births. Obstetrics-Normal and Problem Pregnancies, 4th ed., Copyright® 2002 Churchill Livingstone, Inc. p. 755-763; http://www.wvdhr.org/bph/hp2010/objective/16.htm, May 14, 2003. The use of reproductive technology, the increasing number of pregnancies for women over age of thirty-five, and the growing incidence of multiple births potentially can lead to future increases in this percentage. Furthermore, about 80% of the pre-term births occur spontaneously, while the remainder are induced in response to complications discovered with the fetus or mother. Mattison, D. R.; et al., Pre-term Delivery: a public health perspective, Paediatric and Perinatal Epidemology 2001, 15 (Supple. 2), 7-16.
Infants born pre-term are considerably less physiologically developed than normal term infants. Consequently and as illustrated in FIGS. 1A,B, especially high rates of acute newborn morbidity and mortality are associated with such infants, especially those born extremely pre-term (e.g., 23-27 weeks). These pre-term neonates also face greater risks for long term health problems than infants born full term. Such health problems include underdeveloped respiratory systems, complications to the nervous system, problems feeding, mental retardation, and intraventricular (brain) hemorrhage. Confronting Pre-term Delivery in the 21st Century: From Molecular Intervention to Community Action http://www.medscape.com/viewaarticle/408935. About 60% of all serious prenatal complications or deaths that occur are due to pre-term delivery. Further, pre-term birth also has been associated with several maternal complications including infection due to pre-term rupture of the membrane (PROM) and postpartum depression. The most significant source of maternal risk is associated with the higher rates of caesarean delivery. Premature delivery complicates the level of surgery required which increases the possibility of hemorrhage, thromboembolism and infection.
Pre-term births result not only in high medical risks but also result in higher medical costs, where the major medical costs are typically incurred after delivery. These pre-term newborn infants usually require a much longer hospital stay (e.g., the average hospital stay pf a pre-term infant is 21.7 days) and more expensive treatments than a normal term baby. Such treatments include incubation, respiratory assistance and dialysis. It has been reported that the cost for the care of premature infants is over six billion dollars annually, where about seventy five percent of this value is spent in the first year of life, mostly on the initial hospitalization. Studies to quantify such expenditures also show an inverse correlation between mean cost per surviving infant and the gestational age. As illustration, while a healthy pregnancy costs on average $6,400, the medical costs associated with a pre-term baby can cost $20,000 to $1 million, where the mean cost per infant for infants born between weeks 26-28 is about $49,000.
There are many conditions that may result in pre-term delivery. These include: genetic predisposition, maternal or fetal stress or infection, premature rupture of the amniotic membrane, abnormal hormonal signals, and abnormal uterine properties. Regardless of cause, the softening, dilation, and effacement of the cervix during pregnancy and labor do not occur as a result of uterine contractions alone, but are also a result of an active remodeling of the structure of the cervix. Pre-term labor is often a result of improper timing of the normal signals that trigger cervical remodeling, and pre-term softening of the cervical tissue can result in spontaneous abortion, pre-term delivery, and sometimes impairs normal vaginal delivery.
Regardless of the point during gestation that hormonal signals to remodel arrive, it is believed that they trigger similar changes in the cervix. In the transition to labor, the tissue of the human pregnant cervix undergoes significant remodeling, such that its predominantly collagen matrix is replaced by glycosaminoglycans. As a result of this “ripening,” the cervix softens, thereby preparing for the thinning and dilation that will ultimately be required to allow the fetus to exit the womb.
If detected early enough, there are several treatments that may be very effective in delaying labor until an acceptable gestational age and level of fetal development occurs. These treatments vary from something as simple as bed rest to drugs that can be administered in an effort to postpone labor or arrest its progression. Such drugs include, but are not limited to beta-adrenergic receptor agonists, magnesium sulfate, calcium channel blockers, cyclooxygenase inhibitors, salbumatol, lidocaine and nitric oxide/nitric oxide donors. Corticosteriods also are frequently employed as a specific treatment to the premature fetus to enhance organ maturation as well as improving fetal lung function by speeding development of the lungs and respiratory enzymes necessary for oxygen transfer. These also may decrease the risk of intraventricualar hemorrhage and injury to the gastrointestinal tract. These treatments are more likely to be effective and safe if the onset of pre-term labor is caught early in the gestation period.
Accurate and early diagnosis of pre-term labor is a major problem as up to about 50% of patients being diagnosed with pre-term labor do not actually have pre-term labor and yet as many as 20% of symptomatic patients diagnosed as not being in labor will deliver prematurely. Such misdiagnosis is problematic because, as indicated herein, intervention early in the gestation period is more advantageous to effectively prevent pre-term delivery. Currently, a physician weighs the importance of several parameters such as patient history, biochemical test results, and examination of the cervix, to predict the onset of pre-term labor. For example, a patient history significant for certain obstetrical conditions, such as cervical incompetence, infections of the amniotic fluid, previous abortion or prior pre-term delivery has been shown to increase the risk of pre-term labor in an index or subsequent pregnancy.
The most reliable method of labor prediction involves the obstetrician to digitally palpitating (using his/her finger(s)) the cervix to evaluate its softness. Such examinations can be conducted in 1 to 2 hour intervals until the obstetrician is satisfied that progressive change in the consistency, position, dilation and effacement of the cervix is or is not occurring. This method, in addition to being dependent upon the experience of the obstetrician, is qualitative in nature and therefore large changes in cervical consistency must occur before a changes able to be felt. Obstetricians also can use ultrasound technology to determine the position of the fetus and the length of the cervix, but his data alone is not sufficient to predict whether delivery will occur.
The current absence of diagnostic methods that have acceptable rates of sensitivity and specificity has prompted researchers and others to look for other ways to predict pre-term labor earlier. Many of these methods are based on qualitatively measuring the physical changes, as opposed to biochemical ones, that have been discovered to occur in a cervix of a pregnant woman. More advanced diagnostic methods including transabdominal electromyography (EMG) and transvaginal ultrasound (TVS) do exist and have been shown to slightly increase diagnostic accuracy. Cervical length and force of muscle contractions are examples of how TVS and transabdominal EMG measure physical changes. TVS measures the cervical length using ultrasound wave resonance, which may reflect cervical incompetence. Unfortunately this method does have a number of disadvantages including uncertainty related to the lack of a standard cervical measurement to judge against and variations in cervical length due to filing of the bladder. Another technology that has been used to detect pre-term labor is transabdominal EMG that essentially involves measuring the voltage produced by uterine contractions. The main disadvantage concerning the use of this technique is that childbirth specific uterine contractions tend to occur relatively close to the time of actual delivery (e.g., about 4 days in advance). This, as a practical matter, is much to short for any preventive treatment to have a significant effect on the mother.
Despite the foregoing, it also should be recognized that despite about two decades of improvement in regards to neonatal care, the rate of pre-term birth over that time has not been reduced and has remained essentially at a annual rate of about 11%. Although many reasons for this abound, a significant issue as referred to herein is that by the time the onset of premature labor is recognized clinically, little is available to arrest the process. As such, it is desirous to be able to detect the onset of premature labor well it would become clinically apparent using conventional techniques. This would allow medical intervention to occur earlier in the gestation period than is possible presently and can increase the likelihood that such medical intervention can be more successful in delaying or preventing pre-term delivery as compared to what is possible using existing techniques.
Recently, the focus of a number of studies has been on using biochemical markers as indicators or pre-term labor. Certain concentrations of compounds, such as fetal fibronectin, placental protein, prolactin and estriol found in the serum or vaginal fluid/secretions of the mother would indicate a risk of pre-term delivery. These methods, are still highly experimental and also do not indicate with any certainty whether or not a particular patient will actually deliver pre-term.
In addition to early detection of pre-term labor, it also is desirous to assess the degree of cervical remodeling that can be used to determine the readiness or ripeness of the cervix for labor in general. This determination has important implications for choosing the method for inducing labor when indications to do so develop during the course of a complicated pregnancy. In addition, in the current age of cost containment, it also would be advantageous to have a mechanism by which one can more accurately predict the onset of labor even for pregnancies that go to normal term. This would allow for better planning and staffing of labor and delivery hospital units because anticipated volume of births could be more accurately predicted.
As a non-obstetrical application, it has been suggested that electrical impedance spectra of tissues, more specifically cervical tissue, might be useable as a screening technique for the detection of cervical precancers and more specifically a screening technique whereby there is good separation between normal and precancerous tissues. Brown et al., Relation between tissue structure and imposed electrical current flow in certain neoplasia, Lancet 2000, 335: 892-895. In the described technique a pencil probe with four flush mounted gold electrodes (i.e., mounted flush to face of the probe) was used to measure electrical impedance spectra from eight points on the cervix. The method and apparatus reported, however, was developed to determine the efficacy of the concept and thus are generally experimental in nature.
A comparative study of pregnant cervix and non-pregnant cervix using electrical impedance measurements also has been reported. O'Connel, M P; et al; An in vivo comparative study of the pregnant and non-pregnant cervix using bioelectrical impedance measurements, British Journal of Obstetrics and Gynecology, August 2000, Vol. 107, p. 1040-1041. The article postulates that the electrical impedance techniques could be used to characterize the changes in cervical hydration that precedes labor. The article also postulates that this may be of clinical value in the prediction of labor onset both term and pre-term.
In the described technique a pencil probe with four flush mounted gold electrodes (i.e., mounted flush to face of the probe) was used to measure electrical impedance spectra of the cervix. The study observed a resistivity difference between the tissues of the cervix of women in the delivery suite at the time of induction of labor prior to any intervention and the tissues of the cervix of non-pregnant women. The method and apparatus reported, however, was developed to determine the efficacy of the general concept that there was a noticeable difference between the electrical impedance measured for cervical tissues of women in the later stages of pregnancy and women that are not pregnant As to other described postulated clinical uses, the article merely postulates or suggests that electrical impedance might be useable for such uses but does not include a demonstration or disclosure of the use of a bioimpedance measurement technique for the other suggested and described clinical uses.
It thus would be desirable to provide non-invasive devices, apparatuses, systems and methods that allow a clinician or obstetrician to directly measure the electrical impedance of the cervical tissue of a patient so as to allow the clinician to assess the cervical tissue for obstetrical or non-obstetrical related diagnosis/examination. It would be particularly desirable to provide such a device apparatus, system and method that would allow a clinician to make a determination of the onset of pre term labor earlier in gestation as compared to prior art devices and/or techniques. It also would be desirable to provide systems embodying such devices and apparatuses whereby the measurements can be evaluated so further clinical information (e.g., an out of norm condition indication) is provided by the system to assist the clinician/diagnostician with the examination or diagnosis of a given patient. Such devices, apparatuses and systems preferably would be simple in construction and easy to use by the clinician, diagnostician, or obstetrician. Such devices, apparatuses and methods also preferably would have the beneficial effect of reducing the risk of neonatal mortality from pre-maturity, reducing the risk and/or amount of medical treatment needed for the pre-term infant, and reducing maternal risk. Such devices, apparatuses and methods also preferably would have the beneficial effect of reducing misdiagnosis particularly when compared with what occurs with the use of conventional obstetrical techniques for assessing cervical tissues and/or the risk for onset of pre-term delivery. Such devices, apparatuses, systems and methods also preferably are easily adaptable for use in combination with existing techniques and methods to assess the cervical tissues for non-obstetrical purposes so as to reduce the need to use invasive techniques for assessing cervical tissue (e.g., minimizing cervical bioposies).